\chapter{四边形}

\section{多边形}
\input{units/czjh1-ch4-subsec1}
\input{units/czjh1-ch4-subsec2}
\input{units/czjh1-ch4-xiti12}

\section{平行四边形}
\input{units/czjh1-ch4-subsec3}
\input{units/czjh1-ch4-subsec4}
\input{units/czjh1-ch4-xiti13}

\input{units/czjh1-ch4-subsec5}
\input{units/czjh1-ch4-subsec6}
\input{units/czjh1-ch4-subsec7}
\input{units/czjh1-ch4-subsec8}
\input{units/czjh1-ch4-xiti14}

\section{梯形}
\input{units/czjh1-ch4-subsec9}
\input{units/czjh1-ch4-xiti15}

\input{units/czjh1-ch4-subsec10}
\input{units/czjh1-ch4-subsec11}
\input{units/czjh1-ch4-xiti16}

\input{units/czjh1-ch4-xiaojie}
\input{units/czjh1-ch4-fuxi}

